feat: add button spinner infra.

demo/Semi.Avalonia.Demo/Pages/ButtonSpinnerDemo.axaml.cs

@@ -0,0 +1,50 @@
+using System;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace Semi.Avalonia.Demo.Pages;
+
+public partial class ButtonSpinnerDemo : UserControl
+{
+    public ButtonSpinnerDemo()
+    {
+        InitializeComponent();
+    }
+
+    public void OnSpin(object sender, SpinEventArgs e)
+    {
+        var spinner = (ButtonSpinner)sender;
+
+        if (spinner.Content is TextBlock txtBox)
+        {
+            int value = Array.IndexOf(_mountains, txtBox.Text);
+            if (e.Direction == SpinDirection.Increase)
+                value++;
+            else
+                value--;
+
+            if (value < 0)
+                value = _mountains.Length - 1;
+            else if (value >= _mountains.Length)
+                value = 0;
+
+            txtBox.Text = _mountains[value];
+        }
+
+    }
+
+    private readonly string[] _mountains = new[]
+    {
+        "Everest",
+        "K2 (Mount Godwin Austen)",
+        "Kangchenjunga",
+        "Lhotse",
+        "Makalu",
+        "Cho Oyu",
+        "Dhaulagiri",
+        "Manaslu",
+        "Nanga Parbat",
+        "Annapurna"
+    };
+}